This invention relates to a method for restoration of concrete decks of the type over which vehicles can pass, the method allowing the restoration of the concrete structure while vehicles are allowed to pass over the concrete structure. This method is particularly but not exclusively designed for use with concrete bridge decks so that the concrete can be restored while the bridge is still in normal operation. However the method may also be used in other horizontal concrete structures.
It is known that concrete can be restored by generating movement of ions within the concrete structure between an anode located on the exterior of the concrete structure and a cathode defined by the conventional metal reinforcing members within the concrete. An electrolyte is carried in a porous material between the outside surface of the concrete and the anode.
Various restorative effects can be obtained using this method including particularly the extraction of chloride ions from the concrete which would otherwise cause corrosion of the metal reinforcement leading to degradation of this structure and spalling of the concrete material covering the reinforcing members.
Examples of this method are shown and described in detail in a brochure by Norcure Chloride Removal Systems Inc. entitled "Is Salt Induced Corrosion Causing Problems with your Concrete Structures", in a brochure by Vector Construction entitled "The Concrete Restoration and Protection Specialists" and in a brochure by "Fosroc/NCTAS" entitled "Norcure Desalination". These brochures describe a technique which is used for various concrete structures including bridge decks and the brochure by Fosroc shows particularly a technique in which a bridge deck is restored using this anodic method.
In the brochure and as generally used in practice, after the concrete surface is exposed by removal of any covering layers, a porous material is laid down onto the upper surface and this receives an electrolyte. The porous material is then covered by a mesh type electrode in the form of wire netting which is then covered by a further layer of the porous material.
A current supply is connected between the mesh anode and the reinforcing steel of the concrete and over an extended period of many weeks this acts to cause transfer of ions from the concrete material through the electrolyte to provide a restorative effect.
However the conventional technique using the layers of porous material and the wire mesh anode require that the bridge deck be placed out of operation for the extended period of the restoration. While this can be accommodated in some cases, it does of course severely restrict traffic flow.
The increased usage of salt as a de-icing agent in freezing conditions has severely exacerbated the problem of chloride degradation of concrete.
Up till now, therefore, in practice it has not been possible to operate this technique without the necessity for closing the concrete structure to passing vehicles or traffic and this disadvantage has in effect prevented the use of this restorative technique.
U.S. Pat. No. 5,296,120 (Bennett et al assigned to ELTECH Systems Corporation and issued Mar. 22, 1994) discloses an anode system for use in the above method. However this technique as disclosed in the patent has achieved little or no commercial success and has in effect been abandoned.
The main disclosure of the patent relates to an anode construction which can be rolled into a supply roll for transportation and then can be unrolled into place. The patent also mentions an additional embodiment in which a rigid sheet is applied on top of the unrolled anode structure and supported relative to the anode structure on spacers which hold the rigid plate upward from the horizontal concrete surface and thus prevent the application of forces from the rigid sheet onto the anode structure.
The patent states that the rigid sheet can be non conductive such as wood or plastic. The patent further states that the rigid sheet can be steel, in which case the steel will be in electrical connection to the anode structure and thus will act to some extent as an anode. Such steel anodes are consumed during the electrolytic process and this is advantageous in some circumstances. It is clear however in all circumstances in this patent that the "backing sheet" of steel or other material is intended as an addition to the anode structure including the wire mesh and is intended to be held supported from the underlying concrete surface by spacers to prevent the application of loads to the anode structure itself.
As stated above the techniques disclosed in passing in this patent have not been adopted in practice.
A further example is disclosed in U.S. Pat. No. 5,141,607 issued Aug. 25, 1992 (Swiat assigned to Corrpro Companies Inc). This patent discloses in the embodiment of FIG. 3 a technique for horizontal decks. The anode is a mesh-type anode embedded within a porous material.
This arrangement is the conventional arrangement for this type of process. The applicant is well aware of the work carried out by the assignee of Swiat in the United States around the time of the application. All published material relating to this work is concerned solely with vertical structures of the type shown in FIGS. 1 and 2. It is believed that the work did not include any restoration of horizontal surfaces such as bridge decks. Furthermore it is believed that this work was abandoned and did not lead to any commercial success. In addition to the specific embodiment disclosed, Swiat mentions a number of other alternatives but provides no details of how these may be accomplished.
The prior art therefore discloses a method for restoration of an existing set concrete deck comprising:
providing a generally horizontal load bearing concrete deck having a generally horizontal upper surface over which traffic can pass, the concrete deck having metallic reinforcing elements and the concrete therein being in a set condition; PA1 placing on the horizontal upper surface an electrically conductive anode; PA1 connecting an electrical current between the metallic reinforcing elements as a cathode and the electrically conductive anode so as to cause current to flow therebetween; PA1 providing an electrolyte between the anode and the upper surface so that the current causes movement of ions between the anode and the cathode within the concrete; PA1 providing the electrically conductive anode so as to consist solely of a rigid sheet of a consumable steel material having an upper surface and a substantially planar lower surface which is placed onto the upper surface of the concrete deck with the electrolyte therebetween such that the ions are withdrawn from the concrete into the electrolyte; PA1 attaching the rigid sheet to the deck to prevent movement of the sheet relative to the deck; PA1 causing the traffic to pass over the upper surface of the sheet while the sheet is in place on the concrete deck such that forces from the traffic are communicated through the upper surface to the sheet; PA1 and locating the planar lower surface of the sheet relative to the upper surface of the concrete deck such that, substantially over the full area of the sheet, each point on the lower surface of the sheet receives direct support from a corresponding underlying point on the upper surface of the concrete deck and that forces applied to the upper surface of the sheet by the traffic are communicated directly from the lower surface of the sheet to the upper surface of the concrete deck through the corresponding points.